Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$100.39	4.155%	$104.5612	$104.56	$104.55	$104.60
Purchase #2	$218.43	3.122%	$225.2494	$225.25	$225.25	$225.20
Purchase #3	$80.28	13.251%	$90.9179	$90.92	$90.90	$90.90
Purchase #4	$124.85	10.587%	$138.0679	$138.07	$138.05	$138.10
Purchase #5	$41.63	8.407%	$45.1298	$45.13	$45.15	$45.10
Purchase #6	$201.73	3.851%	$209.4986	$209.50	$209.50	$209.50
Purchase #7	$22.69	11.846%	$25.3779	$25.38	$25.40	$25.40
7 purchase totals =	$790.00		$838.8027	$838.81	$838.80	$838.80